Method for engraving irreproducible pattern on the surface of a diamond

ABSTRACT

The present invention provides a method for engraving desired irreproducible patterns on the surface of gemstones including diamond by the use of an energetic ion beam. The pattern has a characteristic topological texture, which is irreproducible even using the same ion beam to engrave onto the same location of the same diamond.

FIELD OF THE INVENTION

The present invention is in the field of ion beam marking on gemstones, and more specifically on diamonds.

BACKGROUND OF THE INVENTION

Historically, marking of a diamond was not considered practical because it is the hardest material on Earth. Thanks to the invention of modem laser and ion beams, it is now possible to conduct lithography on the surface of diamond using these energetic beams. The mark created on a diamond can be reduced to such a small scale that it is invisible to the naked eye or under the observation of a loupe with a ten times magnification; and it does not affect the clarity or the color grade of the diamond. The mark can also be made so large that it is visible to the naked eye, and certain desired special visual effects can be produced by the lithographic processes to enhance the appeal of a diamond. Such a mark on a diamond can be, for instance, the logo of the company responsible for the cutting, polishing, and setting of the diamond. It can also be the miniaturized signature or even photograph of the jeweler or artist. In principle, the marks created by either laser or ion beam can be used as a form of identification.

Various energetic ion beam marking techniques are known to be employed to produce patterns on a gemstone surface. For example, see U.S. Pat. Nos. 5,773,116 and 6,391,215. U.S. Pat. No. 5,773,116 discloses an ultrahigh vacuum focused ion beam micromilling apparatus and process. Additionally, a durable data storage medium using the micromilling process is disclosed, wherein the durable data storage medium is capable of storing, e.g., digital or alphanumeric characters as well as graphical shapes or characters. U.S. Pat. No. 6,391,215 discloses an information mark invisible to the naked eye which is applied to the polished facet of a diamond gemstone by coating the diamond gemstone surface with an electrically conductive layer so as to prevent the diamond from becoming charged, forming the mark with a focused ion beam, and cleaning the diamond surface with a powerful oxidizing agent to reveal a mark having an appropriate depth. The information mark does not detrimentally affect the clarity or color grade of the diamond.

However, these marking methods are not sufficient for authentication in the sense that an identification mark can be easily forged.

SUMMARY OF THE INVENTION

It is the main purpose of this invention to address the above issue by introducing ion-beam-based lithographic processes that can create irreproducible patterns with a characteristic texture on the nanometer scale. The pattern not only can be used for proving the authenticity of the jewel itself but also that of other precious objects such as watches, sculptures, porcelains, and other art works which have the diamond firmly attached to it.

In accordance with one aspect of the present invention there is provided a method for engraving an irreproducible pattern on the surface of gemstone by controlling the pixel dwell time, exposure sequence, and the incident angle of said energetic ion beam with respect to the surface normal of said gemstone.

In accordance with another aspect of the present invention there is provided a gemstone having a surface on which is a pattern which has been applied using said method.

In accordance with yet another aspect of the present invention there is provided a precious object which is permanently attached to said gemstone.

More specifically, the present invention provides a method for engraving an irreproducible pattern on the surface of a diamond, comprising the step of exposing an energetic ion beam onto the surface of the diamond at an angle from the normal of the surface of about 45°-85°. Preferably, the angle is of about 50°-70°. More preferably, the angle is of about 55°-65°, most preferably the angle is of about 60°. The method may engrave a second pattern on the surface of the diamond. This second pattern may be as large as the area of the surface of the diamond, and may optionally be a photograph, printed character, drawing, or signature.

The energetic ion beam used to engrave the irreproducible pattern may be a focused ion beam. Preferably the diameter of the focused ion beam is about 5 nm.

An alternative method for engraving an irreproducible pattern on the surface of a diamond comprises positioning a mask between an output of an ion beam and the surface of the diamond, and exposing the ion beam on the exposed area of the mask at an angle from the normal of the surface of about 45°-85°. Preferably, the angle is of about 50°-70°. More preferably, the angle is of about 55°-65°, most preferably the angle is of about 60°. The step of positioning a mask may comprise the steps of covering the surface of the diamond with a resist layer; and removing selected portion(s) of the resist layer to expose an area or areas to said energetic ion beam.

The energetic ion beam may be a broad ion beam, such as Ar+.

The present invention also provides for a novel diamond having a surface on which a pattern has been applied using the methods described above.

The present invention also provides a method of authenticating an object by permanently attaching to the object a diamond having a surface on which is a pattern has been applied using the methods described above.

These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings in which:

FIG. 1 is a schematic showing that a FIB is scanned over the predetermined area of a diamond to engrave a desired pattern.

FIG. 2(a) is a schematic showing a logo of the Institute of Atomic and Molecular Sciences,

FIG. 2(b) is a schematic showing a miniature version of the logo engraved on a diamond surface by FIB lithography (full scale of the FIB image is 4 μm).

FIG. 3 is a schematic showing that a broad ion beam is used to sputter remove carbon from the area on a diamond surface that is no longer protected by the resist layer after photolithography is performed.

FIG. 4(a) is a scanning ion microscope image of the fingerprint-like texture produced by the method of the present invention, and

FIG. 2(b) is the detailed topology of the fingerprint-like texture.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

FIG. 1 shows a schematic for one of the processes that can be used to create a pattern on the surface of a diamond. The function of the focused ion beam (FIB) is analogous to a chisel which allows a sculptor to engrave a pattern or symbol onto a stone. By dwelling the FIB over a specific spot on a diamond, certain number (sputtering yield) of carbon atoms is sputtered away from its surface, leaving a small crater with a size approximately equal to the beam diameter of the FIB. Since the current FIB technology can create a beam with a diameter as small as ˜5 nm, it is, in principle, possible to create patterns with ˜10 nm spatial resolution. On the other hand, the size of the entire pattern can be as large as the diamond itself.

In a typical FIB lithographic process, a digital version of the pattern to be created is stored in the computer, which controls the magnification of the pattern to be drawn, the dwell time for each pixel, and sequence of the pixel to be exposed. The sample is always mounted on a stage that can be rotated, tilted, and moved along x-y-z directions. By changing the pixel dwell time, exposure sequence, and the incident angle of FIB with respect to the surface normal of a diamond, it is possible to create a miniature version of the desired pattern with a characteristic texture on the nanometer scale. Preferably, the ion beam is directed onto the surface of the diamond at an angle of about 45°-85° from the normal of the surface. More preferably, the angle is of about 50°-70° or about 55°-65°, and most preferably the angle is of about 60°.

For example, the logo of the Institute of Atomic and Molecular Sciences in Academia Sinica, as shown in FIG. 2(a), is first stored as a digital file in the computer, which then directs the FIB to the desired area and engraved a miniature version of the logo on a diamond surface, as shown in FIG. 2(b). The most important feature to be noted in this image is the fingerprint-like texture on the logo and its surrounding area. The texture is spontaneous formed during the ion bombardment process; and one can only control its general outline and impression rather than the topological details. Specifically, it can not be reproduced even by using the same FIB to conduct the lithography at the exactly identical experimental conditions. It is this irreproducible texture on the nanometer scale that allows us to certify the authenticity of the diamond carrying this unique symbol. Such ‘nano-texture’ is very much like the unique style or patterns that usually appear on the sculptures by a particular sculptor using a specific cutting technique. Another example of this nano-texture is exhibited in FIG. 4, which shows a scanning ion microscope image of the nano-texture along with a determination of its topography.

An alternative way, as shown in FIG. 3, in order to create a nano-textured pattern on a diamond is to have its surface first covered by a resist layer, then photolithography is used to expose the area that is to be sputtered by the broad ion beam such as Ar+. Depending on the conditions used for the ion sputtering, patterns with characteristic nano-texture similar, but not identical, to that produced by FIB-sputtering can also be created on the diamond.

The third method is to combine the high speed of a broad ion beam and the high precision of focused ion beam to create a combination of large and small patterns with different characteristic nano-texture on the surface of diamond. With its high throughput and precision, such a hybrid patterning process would certainly be the most desirable way for a large scale manufacturing.

Once a diamond is marked with irreproducible nano-textured patterns, it can also be used to certify the authenticity of other precious objects such as art works. For example, the diamond can be firmly attached to watches, sculptures, or porcelains to not only enhance their beauty but also certify their authenticity. Depending on the material of the object to be certified, there are various ways to permanently attach the diamond to its surface. As used herein, a permanent attachment is defined as the formation of a strong bond between two objects such that any attempt to separate them would result in the damage of one or the other.

The invention is not limited by the embodiments described above which are presented as examples only but can be modified in various ways within the scope of protection defined by the appended patent claims. All cited references are herein incorporated by reference in their entirety. 

1. A method for engraving an irreproducible pattern on the surface of a diamond, comprising the step of: exposing an energetic ion beam onto the surface of the diamond at an angle from the normal of the surface of about 45°-85°.
 2. The method according to claim 1 wherein the angle is of about 50°-70°.
 3. The method according to claim 1 wherein the angle is of about 55°-65°.
 4. The method according to claim 1 wherein the angle is of about 60°.
 5. The method according to claim 1 further comprising the step of engraving a second pattern on the surface of the diamond.
 6. A method according to claim 5 wherein the size of the entire said second pattern can be as large as the area of the surface of the diamond.
 7. The method according to claim 5 wherein said second pattern is at least one selected from the group consisting of a photograph, printed character, drawing, and signature.
 8. The method according to claim 1 wherein said energetic ion beam is a focused ion beam.
 9. The method according to claim 8 wherein the diameter of said focused ion beam is about 5 nm.
 10. A method for engraving an irreproducible pattern on the surface of a diamond, comprising the steps of: positioning a mask between an output of an ion beam and the surface of the diamond; and exposing the ion beam on the exposed area of the mask at an angle from the normal of the surface of about 45°-85°.
 11. The method according to claim 10 wherein the angle is of about 50°-70°.
 12. The method according to claim 10 wherein the angle is of about 55°-65°.
 13. The method according to claim 10 wherein the angle is of about 60°.
 14. The method according to claim 10 wherein the step of positioning a mask comprises the steps of: covering the surface of the diamond with a resist layer; and removing selected portion of the resist layer to expose an area to said energetic ion beam.
 15. The method according to claim 10 wherein said energetic ion beam is a broad ion beam.
 16. The method according to claim 15 wherein said broad ion beam is Ar+.
 17. A diamond having a surface on which is a pattern has been applied using the method comprising the step of: exposing an energetic ion beam onto the surface of the diamond at a angle from the normal of the surface of about 45°-85°.
 18. A method of authenticating an object comprising permanently attaching to the object a diamond according to claim
 17. 